CN113549826A

CN113549826A - Marine steel with excellent CTOD (weld joint diameter) performance and manufacturing method thereof

Info

Publication number: CN113549826A
Application number: CN202110788234.7A
Authority: CN
Inventors: 金耀辉; 赵坦; 韩鹏; 朱隆浩; 王�华; 于浩男; 李家安; 陈华; 渠秀娟; 柴铁洋
Original assignee: Angang Steel Co Ltd
Current assignee: Angang Steel Co Ltd
Priority date: 2021-07-13
Filing date: 2021-07-13
Publication date: 2021-10-26
Anticipated expiration: 2041-07-13
Also published as: CN113549826B

Abstract

The invention relates to marine steel with excellent CTOD performance of a welding joint and a manufacturing method thereof, wherein the steel comprises the following chemical components in percentage by weight: 0.07 to 0.12 percent of C, 0.05 to 0.15 percent of Si, 1.35 to 1.65 percent of Mn, less than or equal to 0.012 percent of P, less than or equal to 0.003 percent of S, less than or equal to 0.25 percent of Cu, 0.15 to 0.35 percent of Ni, 0.1 to 0.25 percent of Cr0.1, 0.05 to 0.15 percent of Mo0.05, 0.010 to 0.030 percent of Ti0.010, 0.004 to 0.008 percent of N, less than or equal to 2.5 percent of Ti/N, less than or equal to 0.0020 percent of O, 0.01 to 0.025 percent of Als, 0.010 to 0.030 percent of Ce, and the balance of Fe and inevitable impurities. The CTOD of the steel plate welded joint at the temperature of-10 ℃ is more than or equal to 0.38 mm.

Description

Marine steel with excellent CTOD (weld joint diameter) performance and manufacturing method thereof

Technical Field

The invention relates to the field of steel material preparation, in particular to marine steel with excellent CTOD (welded joint diameter) performance and a manufacturing method thereof.

Background

The steel is used as a key structural material of ocean engineering equipment and widely applied to offshore wind power, production platforms, submarine pipelines and the like. The service environment of the steel plate for the offshore structure is severe, the steel plate not only needs to bear gravity load, but also needs to bear wind load, wave load, ocean current load, ice load and earthquake load, the service period of the marine engineering equipment is 50% longer than that of ships, the requirement on steel materials is extremely high, the thickness of the steel plate used by the platform structure is continuously increased along with the development of the marine engineering equipment to extreme service environments such as deep and far sea, extremely cold environment and the like, and the possibility of brittle failure of the steel plate and the welding joint part is increased more and more. The CTOD (crack tip opening displacement) test has been widely used for evaluating the toughness of thick steel plates for maritime work. In order to ensure that the marine engineering equipment can withstand impact and collision of an offshore ice block, the marine engineering equipment is required to have good mechanical properties, particularly the performance of a steel plate base metal and a welded joint CTOD (carbon steel plate oxide) and to meet the requirement of ocean engineering on a high-performance ultrahigh-strength low-temperature steel plate, the ultrahigh-strength marine steel with excellent performance of the welded joint CTOD is urgently required to be developed.

The patent document CN102732781B discloses that "a steel for ocean platform with CTOD at-40 ℃ being more than or equal to 2mm and a production method thereof" combines a low-carbon, ultra-low manganese, low-titanium and low-aluminum component system, and adopts TMCP technology to produce the steel for ocean engineering with CTOD at-40 ℃ being more than or equal to 2 mm. But the maximum finished thickness is only 60mm, and the CTOD performance of the welding joint is not involved, so that the application range of the welding joint is limited.

Patent document CN105579602B discloses a steel sheet having excellent CTOD properties at a multi-layer welded joint, which is produced by TMCP + T process and controlled by the grain size of the base material and the size of the composite inclusions. But the alloy cost is higher; the temperature point of part of the control temperature is the central temperature of the plate thickness, which is not beneficial to field implementation and popularization, and the delivery state of TMCP + T can not meet the requirement of part of users on delivery of the quenched and tempered state.

Patent document CN101578384B discloses "steel excellent in CTOD properties in a weld heat affected zone and manufacturing method thereof" provides a high-strength steel having excellent CTOD (fracture toughness) properties not found so far, which satisfies the CTOD properties in an IC part in addition to the CTOD properties in an FL part at-60 ℃ in multilayer welding of small to medium line energies, and manufacturing method thereof, by using a CR/TMCP/DQ process. However, the Mn content is high, MnS is easily formed to influence impact toughness, the content of noble alloys such as Ni element is high, the alloy cost is high, the maximum thickness is only 60mm, and the application range is limited.

From the above comparison documents, the currently available marine steel with excellent CTOD performance has the following disadvantages:

1) the product has small thickness specification and narrow application range;

2) the delivery state of the product is single, most of the products are delivered in TMCP/TMCP + T states, and the requirements of part of customers on quality-adjusting delivery cannot be met;

3) the alloy has higher cost and difficult field control, and is not beneficial to large-scale production and popularization.

Disclosure of Invention

The invention aims to provide marine steel with excellent CTOD (welded joint) performance and a manufacturing method thereof, and the marine steel is designed by the content of low-precious metal alloy, is added with trace rare earth element Ce, and is designed by coupling alloy composition design-smelting-deformation-heat treatment process, so that a finished product of the marine steel plate with the thickness of 60-100mm, the low-temperature impact toughness at-40 ℃ and the CTOD performance at-10 ℃ for the welded joint is finally obtained. The steel plate has the characteristics of ultrahigh strength (the yield strength is more than or equal to 420MPa, the tensile strength is 500-640 MPa, the elongation after fracture is more than or equal to 19%), excellent low-temperature toughness (the impact energy at minus 40 ℃ is more than or equal to 100J), CTOD performance at minus 10 ℃ of a welded joint is more than or equal to 0.38mm, and uniform structure performance.

In order to achieve the purpose, the invention adopts the following technical scheme:

the marine steel with excellent CTOD performance of the welding joint comprises the following chemical components in percentage by weight: 0.07 to 0.12 percent of C, 0.05 to 0.15 percent of Si, 1.35 to 1.65 percent of Mn, less than or equal to 0.012 percent of P, less than or equal to 0.003 percent of S, less than or equal to 0.25 percent of Cu, 0.15 to 0.35 percent of Ni, 0.1 to 0.25 percent of Cr, 0.05 to 0.15 percent of Mo, 0.010 to 0.030 percent of Ti, 0.004 to 0.008 percent of N, less than or equal to 2.5 percent of Ti/N, less than or equal to 4 percent of O, 0.01 to 0.025 percent of Als, 0.010 to 0.030 percent of Ce, and the balance of Fe and inevitable impurities.

The action mechanism of each alloy component in the steel is as follows:

c: the carbon content is increased, so that the plasticity, low-temperature toughness and welding crack resistance sensitivity of the steel plate are obviously reduced, the carbon content is low, the hardness and strength of the steel after quenching and tempering are low, but the plasticity and toughness are high. From the viewpoint of economy and product performance, the C content is preferably controlled to 0.07% to 0.12%.

Si: solid solution strengthening elements are used for improving the strength of the steel in a solid solution strengthening mode, deoxidizing elements are used, when the deoxidizing effect is influenced by too low silicon content, the surface quality, the toughness and the welding performance are adversely influenced by too high silicon content, and the preferable range of the Si content is 0.05-0.15 percent in comprehensive consideration.

Mn: when the deoxidizer is dissolved in austenite, the critical transformation temperature can be reduced, so that the steel matrix structure can be refined, the deoxidizer is an essential element for ensuring the strength and toughness of steel, and Mn is a good deoxidizer. An appropriate amount of manganese improves the strength and toughness of the steel, but too high results in segregation in the cast slab, which in turn causes bands of structure that are difficult to eliminate after rolling, reducing the core properties and lamellar tear resistance of the steel sheet. In order to ensure the toughness of the material, the Mn content of the material is 1.35-1.65%.

P: the P content is controlled to be not more than 0.012 percent.

S: the S content is controlled to be not higher than 0.003 percent.

Cu: cu mainly plays a role in solid solution strengthening and precipitation strengthening in steel, and a proper amount of Cu improves the strength without damaging the impact toughness. Cu also belongs to an austenite forming element, and promotes the formation and stability of austenite in the tempering process while expanding an austenite phase region. When the Cu element is too high, the hot brittleness phenomenon can be caused, and the toughness of the base material and the heat affected zone is not facilitated, so that the Cu content range is less than or equal to 0.25 percent.

Ni: ni has the solid solution strengthening effect, can promote the alloy steel to form a stable austenite structure, has the characteristics of minimizing the Ar3 point and the increase of the carbon equivalent or the cold crack sensitivity coefficient Pcm, and can improve the strength and the toughness of the steel, so the Ni content is controlled to be 0.15-0.35 percent.

Cr: the important element for improving the hardenability of the steel is that the hardenability can be effectively improved by adding a proper amount of Cr content to the steel for thick ship plates and ocean platforms so as to make up for the strength loss caused by thickness and improve the uniformity of performance in the thickness direction; cr can also enhance the tempering stability of steel, and Cr can generate carbide precipitation with C to enhance the strength of the steel. However, the addition of too high chromium and manganese to the steel at the same time results in the formation of low melting point Cr-Mn complex oxides, surface cracks during hot working, and severe deterioration of weldability. Therefore, the Cr content of the invention is controlled to be 0.1-0.25%.

Mo: the hardenability and the heat strength can be improved, the tempering brittleness can be prevented, and the material strength can be effectively improved; the phase transition temperature is reduced, the critical cooling rate requirement of bainite transformation is reduced, the bainite transformation is promoted in a wider cooling rate range, the thick steel plate has better process adaptability, and the stability of the strength and toughness in the thickness direction of the steel plate can be effectively improved. Therefore, the Mo content of the invention is controlled to be Mo: 0.05 to 0.15 percent.

Ti: TiC and TiN precipitated from the steel can perform grain refinement and precipitation strengthening, improve the anisotropy of the steel plate and eliminate temper brittleness at the same time. However, if the Ti content is too high, coarse square or rectangular Ti (C, N) is precipitated, which is not easily deformed, and stress is concentrated near Ti (C, N) particles when the steel sheet is subjected to stress, which becomes a nucleation growth source of micro-cracks, thereby lowering the toughness of the steel sheet. The preferable content of Ti element in the invention is controlled between 0.010 percent and 0.030 percent.

N: can be matched with Ti element to form fine and dispersed TiN precipitation, and can effectively control the growth of original austenite grains. The quantity of TiN in the steel at high welding temperature is increased, and the inhibiting capability of the material on the austenite grain coarsening tendency in the welding process is improved. However, when the content of dissolved N is too large, the thermoplasticity of the steel material decreases, and the toughness of the steel sheet decreases. Therefore, the N content is 0.004-0.008%.

O: the steel is an element which brings adverse effects on impact toughness and CTOD performance, and is combined with other elements in steel to generate non-metallic inclusions which become crack sources, and the content of O in the steel is controlled to be not higher than 0.002%.

And Als: deoxidizing and refining grain elements, wherein Al element forms fine AlN precipitation at high temperature, and inhibits austenite grains from growing when a plate blank/steel plate is heated to austenitize, thereby achieving the purposes of refining the austenite grains and improving the toughness of the steel at low temperature. The Al content is too high, which causes the formation of larger Al oxide and reduces the low-temperature impact property of the steel plate, and the casting blank is easy to generate corner cracks in the continuous casting process, so the preferred content range of Alt in the invention is 0.010-0.025%.

Ce: the Ce added into the steel can reduce the content of harmful element O, S in the steel, denature sulfide and change strip-shaped manganese sulfide into spherical or ellipsoidal rare earth sulfide. The Ti (C, N) precipitates with large size and hard edges and corners in the steel can be effectively modified by adding the Ti element, so that Ti (C, N) inclusions in the steel are distributed in a fine, round and dispersed manner, and the low-temperature toughness and the CTOD performance of the steel plate are improved. The preferred content range of Ce in the invention is 0.010% -0.030%.

The CTOD of the marine steel plate welded joint at-10 ℃ is more than or equal to 0.38 mm.

The thickness of the finished marine steel plate is 60-100 mm.

The manufacturing method of the marine steel with excellent CTOD performance of the welding joint comprises the following steps:

1) smelting and continuous casting processes: selecting smelting raw materials, carrying out production by adopting molten iron deep desulfurization, converter smelting, external refining, vacuum treatment and continuous casting processes, controlling the content of elements such as P, S and the like as low as possible, controlling the smelting components according to a target value, strictly controlling the content of residual elements, controlling the high cleanliness and cast state structure of a bloom in the smelting and continuous casting processes, protecting and casting the molten tundish at the target superheat degree of 22-28 ℃ in the whole process, putting the continuous casting process under a light pressure, wherein the light pressure is 5-9 mm, and the continuous casting pulling speed is 0.8-1.2/m/min, thus obtaining a continuous casting blank, wherein the thickness of the casting blank is 250-360 mm, and the continuous casting blank is subjected to stacking and slow cooling after being taken off a production line, the stacking temperature is more than or equal to 650 ℃, and the stacking time is more than or equal to 60 hours;

2) the rolling process comprises the following steps: the soaking temperature of the plate blank is controlled to be 1150-1180 ℃, a two-stage controlled rolling technology is adopted in the rolling process, the starting rolling temperature of one stage is 950-1000 ℃, and the single-pass reduction rate of longitudinal rolling is more than or equal to 15% except for widening passes; controlled rolling is adopted in the second stage, the initial rolling temperature of the second stage is 830-880 ℃, the final rolling temperature is 800-850 ℃, the single-pass minimum reduction rate of the second stage is more than or equal to 12%, the accumulated reduction rate is 50-60%, slow cooling is carried out on the rolled steel in a slow cooling groove, the temperature of the rolled steel in the groove is not lower than 350 ℃, and the slow cooling time is not less than 24 hours; controlling the phase change structure to be evenly refined by two-stage rolling, and preparing an initial structure for modulation heat treatment;

3) quenching process: carrying out quenching heat treatment on the steel plate, wherein the quenching heating temperature is controlled to be 880-910 ℃, the temperature rise time is 1.3-1.6 min/mm x the thickness of the steel plate, and the temperature is kept for 20-40 min;

4) and (3) tempering process: and (3) tempering the steel plate, wherein the tempering temperature is 600-650 ℃, the furnace time is 3-4.5 min/mm x the thickness of the steel plate, and the steel plate is air-cooled after being taken out of the furnace to obtain a steel plate finished product.

After the continuous casting blank in the step 1) is off-line, hot acid etching (the etching solution is 1:1 hydrochloric acid aqueous solution, the temperature is 75 +/-5 ℃, the etching time is 40min) is adopted for evaluation, and the evaluation is carried out according to a Mannesmann standard map, wherein the evaluation result is not more than 2 grade.

Compared with the prior art, the invention has the beneficial effects that:

1) the steel plate product produced by the process is subjected to cleaning smelting such as low S, P, O, casting blank segregation and rolled steel plate grain size are controlled by combining a specific continuous casting process and a rolling process, austenitizing (heating) and tempering fine control are performed, and a proper amount of trace rare earth element Ce modified inclusion is particularly added, so that the CTOD (carbon to oxygen ratio) of a steel plate welded joint at-10 ℃ is more than or equal to 0.38 mm.

2) The invention gives full play to the technical equipment advantages of the wide and thick plate rolling mill, combines with the continuous casting slab with the thickness of 250-360 mm, and develops the marine steel thick plate finished product with excellent CTOD performance of the welding joint, wherein the thickness range of the marine steel thick plate finished product is 60-100 mm.

3) Compared with the TMCP or TMCP + T process of the steel plate with the same strength, the off-line quenching can accurately control the quenching temperature, and the temperature of the whole plate is uniform; meanwhile, compared with TMCP or TMCP + T process, the off-line quenching and tempering process is easier to control the plate flatness, and the unevenness of the steel plate within 2 meters is less than or equal to 5 mm.

4) The steel plate has fine and uniform crystal grains, uniform low-temperature impact toughness at different positions in the thickness direction and easy realization of the manufacturing process.

Drawings

FIG. 1 is a photograph (200 times) of a metallographic structure of example 1.

Detailed Description

The following examples are intended to illustrate the invention in detail, and are intended to be a general description of the invention, and not to limit the invention.

The chemical compositions of the steels of the examples of the invention are shown in table 1; the parameters of the smelting and continuous casting processes of the steel and the casting blank evaluation results of the embodiment of the invention are shown in the table 2; the steel plate rolling process of the embodiment of the invention is shown in Table 3; the heat treatment process of the steel plate of the embodiment of the invention is shown in Table 4; the mechanical properties of the steel plate of the embodiment of the invention are shown in Table 5; the welding properties of the steel of the embodiment of the invention are shown in Table 6; CTOD properties of a steel plate welding joint in the embodiment of the invention are shown in Table 7; the unevenness of the steel sheet of the examples of the present invention is shown in Table 8.

TABLE 1 chemical composition wt% of steel of examples of the invention

Examples	C	Si	Mn	P	S	Cu	Ni	Cr	Mo	Ti	Als	Ce	N	O	Ti/N
																1	0.114	0.13	1.36	0.009	0.001	0.16	0.31	0.141	0.142	0.015	0.022	0.015	0.0059	0.0011	2.54
2	0.091	0.15	1.51	0.009	0.002	0.17	0.34	0.131	0.131	0.024	0.014	0.023	0.0070	0.0009	3.43
																3	0.071	0.08	1.61	0.008	0.002	0.15	0.29	0.152	0.149	0.019	0.017	0.016	0.0068	0.0013	2.79
4	0.106	0.14	1.44	0.007	0.001	0.21	0.21	0.127	0.129	0.023	0.019	0.017	0.0058	0.0008	3.97
																5	0.113	0.09	1.41	0.008	0.002	0.13	0.26	0.109	0.112	0.027	0.011	0.025	0.0076	0.0012	3.55
6	0.082	0.14	1.52	0.01	0.003	0.23	0.25	0.183	0.126	0.029	0.012	0.026	0.0089	0.0014	3.26
																7	0.08	0.15	1.49	0.011	0.003	0	0.22	0.191	0.117	0.012	0.023	0.012	0.0046	0.001	2.61
8	0.075	0.15	1.63	0.012	0.002	0	0.17	0.229	0.089	0.017	0.015	0.019	0.0062	0.0007	2.74

TABLE 2 evaluation results of smelting and stacking process parameters and casting blank of steel according to the present invention

Table 3 rolling process of steel plate according to the embodiment of the present invention

TABLE 4 Heat treatment Process of steels of examples of the present invention

TABLE 5 mechanical Properties of steels according to examples of the invention

TABLE 6 weldability of steels of examples of the invention

TABLE 7 CTOD Properties of Steel welded joints according to examples of the present invention

TABLE 8 unevenness of steel sheets according to examples of the present invention

Examples	Measuring the unevenness/mm of a 2000mm long steel plate
		1	2
2	3
		3	3
4	2
		5	3
6	2
		7	3
8	4

。

Claims

1. The marine steel with excellent CTOD performance of the welding joint is characterized in that the steel comprises the following chemical components in percentage by weight: 0.07 to 0.12 percent of C, 0.05 to 0.15 percent of Si, 1.35 to 1.65 percent of Mn, less than or equal to 0.012 percent of P, less than or equal to 0.003 percent of S, less than or equal to 0.25 percent of Cu, 0.15 to 0.35 percent of Ni, 0.1 to 0.25 percent of Cr, 0.05 to 0.15 percent of Mo, 0.010 to 0.030 percent of Ti, 0.004 to 0.009 percent of N, less than or equal to 2.5 percent of Ti/N, less than or equal to 4 percent of O, 0.01 to 0.025 percent of Als, 0.010 to 0.030 percent of Ce, and the balance of Fe and inevitable impurities.

2. The marine steel with excellent CTOD performance of the weld joint as recited in claim 1, wherein the CTOD at-10 ℃ of the marine steel plate weld joint is not less than 0.38 mm.

3. The marine steel with excellent CTOD performance of the weld joint as recited in claim 1, wherein the thickness of the finished marine steel plate is 60-100 mm.

4. A method for manufacturing marine steel having a weld joint with excellent CTOD properties according to any one of claims 1 to 3, comprising the steps of:

1) the rolling process comprises the following steps: the soaking temperature of the plate blank is controlled to be 1150-1180 ℃, a two-stage controlled rolling technology is adopted in the rolling process, the starting rolling temperature of one stage is 950-1000 ℃, and the single-pass reduction rate of longitudinal rolling is more than or equal to 15% except for widening passes; the initial rolling temperature of the second stage is 830-880 ℃, the final rolling temperature is 800-850 ℃, the minimum reduction rate of a single pass of the second stage is more than or equal to 12%, the cumulative reduction rate is 50-60%, the temperature of the slow cooling groove after rolling is not lower than 350 ℃, and the slow cooling time is not less than 24 hours;

2) quenching process: controlling the quenching heating temperature to be 880-910 ℃, keeping the temperature for 20-40 min, wherein the temperature rise time is 1.3-1.6 min/mm x the thickness of the steel plate;

3) and (3) tempering process: tempering temperature is 600-650 ℃, furnace time is 3-4.5 min/mm steel plate thickness, and air cooling is carried out after discharging to obtain a steel plate finished product.

5. The manufacturing method of marine steel with excellent CTOD performance of the weld joint as claimed in claim 4, further comprising the following smelting and continuous casting processes: the target superheat degree of the tundish molten steel is 22-28 ℃, soft reduction is put into the continuous casting process, the soft reduction amount is 5-9 mm, the continuous casting pulling speed is 0.8-1.2 m/min, a continuous casting blank is obtained after continuous casting, the thickness of the casting blank is 250-360 mm, the continuous casting blank is stacked and slowly cooled after being taken off the line, the stacking temperature is greater than or equal to 650 ℃, and the stacking time is greater than or equal to 60 hours; after the continuous casting billet is off-line, the hot acid etching is adopted for evaluation, the evaluation is carried out by referring to a Mannesmann standard map, and the rating result is less than or equal to level 2.